Rob McGinnis recently moved to Santa Cruz and now drives around town in a VW Golf with a rack for a surfboard on top. Like many automobiles, the car is both a form of transportation and a way for its owner to communicate some vital part of his identity. “I used to drive a Tesla Roadster,” he said. ”But now I’m making gasoline cool again.”

Suffice to say that gasoline — a prominent contributor to climate change — is not considered very cool right now in places like Santa Cruz, a reliably liberal town that is in the process of being swallowed by the Pacific Ocean. McGinnis’ plan to resuscitate the fuel’s social standing hinges on a machine he’s building that creates usable gasoline from thin air — rather than from the oil deposits deep underground.

He’s one of a growing number of entrepreneurs pursuing direct carbon capture technology, which extracts carbon from the air and water and transforms it into usable substances such as gasoline, construction materials and industrial chemicals. Like standard fossil fuels, McGinnis’ fuel would release carbon into the air when burned — but not any more than his machine removed to make it. In theory, it’s a circular process that could keep his Golf powered up indefinitely, with no effect on greenhouse gas levels.

Experts increasingly believe that any serious response to climate change must include proactively removing carbon from the atmosphere. Last fall, the United Nations’ Intergovernmental Panel on Climate Change for the first time described carbon removal as “essential.” And while there are a few carbon-removal strategies, direct air carbon capture is the process that has most captured the public imagination. The basic science of this approach has been understood for decades, but it’s an open question as to when — or if — it will be possible to capture airborne carbon at a scale that could make a difference.

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Almost immediately after the U.N. report, the renowned early-stage investment firm Y Combinator made a show of calling for new companies working on carbon removal. The firm, famous for its role in nurturing software companies such as Airbnb Inc., Dropbox Inc. and Stripe Inc., said it was interested in projects that were “risky, unproven, even unlikely to work” and suggested exotic ideas, such as building huge reservoirs in the desert stocked with genetically modified phytoplankton. “It’s time to take big swings at this,” Y Combinator wrote in its call to action.

McGinnis’ company, which he named Prometheus, was offering exactly the kind of classic moonshot Y Combinator seemed to be seeking: a farfetched idea that made sense on paper and could change everything on the off chance it developed beyond that. When Y Combinator sorted through the dozens of pitches it received, his was one of just two in which it decided to invest.

McGinnis brought his machinery — a 6-foot-tall box with several doors held closed by padlocks — to Y Combinator’s semiannual Demo Day in March. The event, a two-day marathon of start-up pitches, is attended by some of the most high-profile investors in the world. McGinnis told the crowd he’d be making fuel that he could sell at a profit by as early as next year.

This was exactly the sort of thing people wanted to hear, according to Gustaf Alströmer, a Y Combinator partner who’s working on its carbon project. “If you say, ‘I’m making gasoline,’ even if there’s a one in 500 or one in 1,000 chance it actually works, you will resonate very well with investors,” he said. Within weeks, McGinnis had raised enough money to hire several people and begin planning to move beyond a single prototype machine.

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McGinnis took an unusual path to being an alternative-fuel evangelist. He attended Yale as an undergraduate theater major, where he wrote plays he described as “techno-optimistic, strange, mini epics.” In his spare time, he built his own desalination machine. The side project eventually inspired him to leave the theater and get a PhD in chemistry.

Eventually, his desalination hobby turned into a desalination company. He was successful enough that he bought that Tesla, along with a vanity license plate carrying the company name: Oasys. McGinnis then launched a second start-up that made materials useful for separating chemicals into their chemical components. The membranes, known as carbon nanotubes, allowed him to conduct several steps of the separation process while the carbon was still in liquid form — making the process significantly cheaper. That idea gives Prometheus its competitive edge.

McGinnis’ breakthrough struck Matt Eisaman, an assistant professor in the engineering department at Stony Brook University, whose research had been the basis of an effort by Google X to create fuel from seawater. The two-year project, which ended in 2016 and was dubbed Foghorn, succeeded in making fuel. But Google nixed it anyway because it saw no clear path to make its product at competitive prices.

Foghorn had been working with carbon and hydrogen at high temperatures in gaseous form, and Eisaman saw McGinnis’ work as a potential step forward. “I’ve seen a lot of attempts of, ‘How do you make a carbon-neutral fuel cost effective?’” he said. ”I can get a good sense early on if there’s a chance.”

Eisaman signed onto Prometheus as an advisor, but he remains cautious about its chances. When asked whether he thinks anyone can figure out a carbon-to-fuel process that will be economic at large scale, Eisaman paused for a long time. ”I don’t know,” he said.

McGinnis, of course, is considerably more bullish. He predicts he’ll be selling a small amount of gasoline by next year in the $3-per-gallon range. McGinnis acknowledges that reaching a scale vast enough to make a difference in the climate remains dauntingly expensive. He estimates that it would cost $800 billion to replace the U.S. gasoline market with carbon-neutral fuel. But there’s no need to wait. Prometheus can sell any gasoline it makes into markets that already exist, and it can be used to power automobiles that were made to burn conventional fuel.

To some, that sounds too easy. The proposal to solve climate change with minimal behavioral or infrastructure changes is the kind of silver-bullet thinking that has led some environmentalists to remain skeptical of carbon removal. In December, former Vice President Al Gore called the entire idea of carbon capture ”nonsense” and likened relying on it to believing in the tooth fairy.

But Julio Friedmann, senior research scholar at the Center on Global Energy Policy at Columbia University, has been studying carbon management for nearly two decades and says ridiculing seemingly off-the-wall experiments is counterproductive. It’s unclear which technologies will make the jump from science project to commercial product, so it’s worth trying everything.

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“There are many companies that have broken their spears on this,” he said. “There are so many companies that were like, ‘We’re going to make something that’s going to compete with gasoline,’ and they’re dead.” Friedmann declined to comment specifically on Prometheus’ technology. But he did say that in the race to replace traditional fuels, time is of the essence: “If it takes us 70 years to displace the incumbent, we lose. That’s not good.”

In March, McGinnis showed his machine to this reporter in the Santa Cruz co-working space where he built it. After cautioning against taking photos, he opened it up, enthusing over the cooling system, showing off the nanotubes that did the chemical separation, and pointing out the spigot at the bottom where the gasoline would come out.

Every part of his system had already been proved to function. But whether the entire thing would work as he hoped it would — or on the timeline he anticipated — remained an open question. Had Prometheus made enough gasoline to power his Golf even a single mile? ”No. No,” he said. ”We just finished the machine on Friday.”